Process for lessening curling tendencies of photographic films



Sept. 6, 1927. 1, 01

A. F. SULZER PROCESS FOR LESSENING CURLING TENDENGIES OF PHOTOGRAPHIC FILMS Filed May 20, 1924 JTTOJLNEY ularly noticeablev where the back face of Patented Sept. 6, 1927;

UNITED STATES 1,641,401 PATENT OFFICE.

ALBERT F. SULZER, OF ROCHESTER, NEW YORK, ASSIGNOR TO EASTMAN KOD AK COM- PANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK.

PROCESS FOR LESSENING CURLING TENDENCIES OFI'IIOTOGRAPHIC FIL'JYIS.

Application filed Ma an, 1924. Serial No. 714,750.

This invention relates to processes for lessening the curling tendencies of vphotographic films, particularly those filmsm which a film comprising a cellulosic addltlon compound, such as cellulose nitrate, cellulose acetate, or cellulose ether, or a mlxture thereof, supports a light sensitive layer, such as a gelatino-silver hal1demulsion. One object'of the invention is to provide a comparatively inexpensive and easlly controlled process for, at least partially, less ening the curling tendency of such films; Other objects will hereinafter appear.

In the accompanying-draw1ng,- I

Fig. 1 is a diagrammatic fragmentary side elevation of. apparatus in which my process may be carried out, the relative slzes of the parts being exaggerated for the sake of clearness;

Fig. 2 is a fragmentary side elevatlon 0 another form of apparatus in whlch my process may be carried out, the relatlve slzes of the parts being exaggerated for the sake of clearness;

Fig. 3 is a fragmentary side elevation of another form of apparatus in whlch my process may be carried out, the relative sizes of the parts being exaggerated for the sake of clearness. I

Bhotographic films, each comprising a light sensitive photographic. layer carr ed on a filmor support composed essentially of .a cellulosic addition compound in admixture with modifying or plastify ing agents, are Well known in the art. When they are given the usual fluid treatment in photographic baths and then dried, a curling tendency manifests itself This 1s particthe support is free or uncovered. This curling tendency has been counteracted by coating such films on the back with a layer, like gelatine, which shrinks at approximately the same rate as the photographic layer as a result of the treatment in the baths and inthe drying operation. But in the case of some films, it is desirable that the back face (the face opposite the one for the photographic layer) be left uncoated with any material which becomes softened when wet to the extentthat gelatine does. It is to the problem of lessening curling tendencies in such film that my invention is directed.

I have. found that this curling tendency in photographic films of cellulosic addltlon compounds, such as nitrocellulose, cellulose acetate and cellulose ether, can be usefully lessened by applying to the back face of said films a plurality of successive coats of varnish, the. varnish for each coat comprising .a cellulosicaddition product carried in a liquid vehicle containing a solvent of said films. In the preferred embodiment of my invention I employ a'liquid solvent vehicle comprising a mixture of a. volatile film solvent with a non-solvent, the latter being preferably volatile also. Even a single coat of such a varnish has some curl-reducing tendency. Dilute varnishes, containing about 2% of the cellulo'sic compound, -act well.

Since nitrocellulose films areat present ,most widely used, I shall describe one emb'odiment of my invention by .way of illustration in connection with such filIIis, but it will be understood that my invention is not restricted thereto, except as indicated in the appended claims.

Referring to the accompanying drawing,

1 represents a Wheel rotating in the direction of arrow 2 and carrying a film 3 of a cellulosic addition compound, say nitrocels lulose, thereon. The face of the film 3 in contact with the smooth even face or periphery of wheel 1 is the face for supporting the. photographic layer, such as a coating of gelatino-silver halid emulsion. The outer face of the film 3, therefore, constitutes the back to which my curl-lessening coatings are successively applied. This can be done, for instance, by coating wheel 4 cont-acting with supply wheel 5 wholly or .partially immersed in a bath 6 of varnish contained in asuitable tank 7. The layer of varnish applied by the roll 4 to the back of film3 sets rapidly and is, therefore, sufficiently hardened to prevent its being washed away when the film 3 reaches roll 8 which applies a second coating of varnish which it receives from supply roll 9 'par-.

.tially immersed in bath '10 contained in tank 11. The film 3 may be merely passed under. wheel 1 in close contact therewith, or it may be formed on wheel 1 by the usual filmforming methods, the film 3 being suflicient-' 1y hardened and set before it reaches the coating stations represented by rolls 4 and 8. In other words the film is always cured to the extent that the potential curling tendency is present before my process is applied to it. Of course, any equivalent well known varnish-applying devices can be substituted,

as will be understood by those skilled in the art.

1 Another apparatus in which the may betreated by my process before the photographic emulsion is applied theretooisillustrated in Fig, 2, Film 3 passes under rolls 12 and 13,'beneath which are rolls 14: and 15 for applying varnish from baths 16 and 17 contained in .tanks 18 and 19. The distance between rolls'12 and 13 can be varied so as to have the first varnish coating set and dried to the desired extent before it reaches roll 15.. Of course, any of the customary heating and drying devices may be located between rolls 12 and 13 for assisting the rapid setting of the varnish layer.

w WVhile my process may conveniently be applied to the photographic film before the photographic coating is placed thereon, nevertheless my curl-lessening operations may be performed on the back of the film after it is covered with'the sensitized layer.

Thus in Fig. 3, 31 represents a film of cellulosic addition compound bearing upon .its upper face a gelatino-silver halid emulsion, for example. This passes over wheel 20 and wheel 21, the delicate photographic sensitive layer being outward and upward, so that it does not contact with the peripheries of the wheels. The rear face of the film is successively, treated with varnish coatings by.

wheels 22 and 23 from baths 24 and 25 in tanks 26 and 27. 'The distance between the rolls 22-and 23 is designed to allow the first coatingto properly set on thefiat tensioned film before the second coating is applied,

and .any conventional intermediate drying means. can be employed for hastening the evaporation of the volatile ingredients from the coatings. Of course, the wheels in allof the above examplesfare power'driven in the usual way where it'is desirable, and the coat- '\are adjustable to ing rolls or other equivalent coating devices and from the film to vary their effect, as will be understood by those skilled in the art and familar with the customary expedients. The volatile solvents may be drawn off and recovered by any known or preferred means.

As an example of a suitable varnish bath which may be used in each of the above described tanks 8.2% (by'wei'ht) solution of nitrocellulose in a mixture 0 acetone and ethyl alchol is excellent. The acetone and tone and alcohol likewise-has suflicient sol-' vent-power to carry the small percentage of nitrocellulose that is present. For rapid work, a solution of the order of 2% of nitro-- cellulose is very useful;

The curl-lessening action is heightened by the volatile active solvent, acetone, and its action is tempered by the non-solvent, ethyl alcohol, and by the small per cent of nitrocellulose, so that the' film is not impaired under the working conditions described above, although the film and all the coatings mutually adhere with firmness. The relatively thin layers of varnish seem to fix or clinch the comparative freedom from curling tendency brought about by the application of the liquid varnish. I apply the term volatile for. convenience of description hereir3 to liquids which boil at or below about 100". 'One coating of varnish on the back, particularly when the vehicle carrying the cellulosic addition compound is wholly volatile, is useful and, of course, can be applied by any one ofthe hereinabove described coating machines, one of the pair of coating wheels being omitted or temporarily put out of use.

For the maximum .efl'ect, however, a plurality of coatings on the back are recommended, these being applied successively, one on top of the other.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

The. process of lessening the curling tendency in photographic nitrocellulose films, which comprisesapplying to the rear face only thereof a plurality of relatively thin doats of varnish oneon the other, said var- .nishbeing a solution of nitrocellulose in a mixture of a volatile solvent and volatile non-solvent thereof, the proportion of nitrocellulose in said varnish being of theorder of magnitudeof two percent.

Signed at Rochester, New York, this 14th I day of May, 1924.

' ALBERT F. SULZER. 

